1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a transflective type liquid crystal display device operable in a reflection mode and a transmission mode, and a method of manufacturing the same.
2. Discussion of the Related Art
Liquid crystal display devices (LCDs) may be classified into a transmission type LCD and a reflection type LCD. While the transmission type LCD uses a backlight unit as a light source, the reflection type LCD uses an external light (e.g., natural light, artificial light) as a light source, instead of light emitted from the backlight unit.
Due to the use of the backlight unit, the transmission type LCD may display an image even in a dark external environment. However, the transmission type LCD has a drawback of high power consumption.
On the contrary, because the reflection type LCD does not use the backlight unit, it has low power consumption but cannot be used in a place where no external light exists (for example, at night).
To overcome these limitations, a transflective type LCD has been developed.
Because the transflective type LCD has both a reflection region and a transmission region within a unit pixel region, it can perform functions of the transmission type LCD and the reflection type LCD at the same time. Accordingly, because the transflective type LCD may use the light emitted from the backlight unit and the external light, it is not affected by the environment and can reduce power consumption.
FIG. 1 is an exploded perspective view of a related art transflective type LCD, and FIG. 2 is a sectional view of the related art transflective type LCD illustrated in FIG. 1. Referring to FIGS. 1 and 2, the related art transflective type LCD 11 includes a top substrate 15, a bottom substrate 21, liquid crystals 14, and a backlight unit 41. The top substrate 11 includes a black matrix 16, sub color filters 17, and transparent common electrodes 13. The bottom substrate 21 includes switching elements T and array lines 25 and 39 formed in a pixel region P. The liquid crystals 14 are injected between the top substrate 15 and the bottom substrate 21. The backlight unit 41 is disposed under the bottom substrate 21.
The pixel region P has a transmission region B and a reflection region D. The transmission region B and the reflection region D are defined by a reflective electrode 49 and a transparent electrode 61. The transmission region B has a transmission hole A in which the reflective electrode 49 is not present. The reflective electrode 49 exists in the reflection region D.
An operation of the related art transflective type LCD in the reflection mode and in the transmission mode will be described below.
In the reflection mode, external light is used as the light source. In this case, light F2 incident on the top substrate 15 is reflected from the reflective electrode 49 and passes through liquid crystals 14 arranged according to an electric field between the reflective electrode 49 and the common electrode 13. The amount of the light F2 passing through the liquid crystals 14 is adjusted according to the arrangement of the liquid crystals 14 and thereby an image is displayed.
In the transmission mode, the backlight unit 41 disposed under the bottom substrate 21 is used as the light source. Light F1 emitted from the backlight unit 41 is incident on the liquid crystals 14 through the transparent electrode 61 and the transmission hole A. Then, the light F1 passes through the liquid crystals 14 arranged according to an electric field between the transparent electrode 61 and the common electrode 13. An amount of the light F1 passing through the liquid crystals 14 is adjusted according to the arrangement of the liquid crystals 14 and thereby an image is displayed.
FIG. 3 is an enlarged plan view of a portion of the bottom substrate in the related art transflective type LCD.
The bottom substrate 21 is also called an array substrate. The bottom substrate 21 includes a plurality of gate lines 25, a plurality of data lines 39, and thin film transistors (TFTs) T. The gate lines 25 and the data lines 39 cross one another. The TFTs T acting as switching elements are provided at crossings of the gate lines 25 and the data lines 39. Pixel regions P are defined by the crossing of the gate lines 25 and the data lines 39.
A gate pad electrode 27 is formed at one end of the gate line 25 and has a larger width than that of the gate line 25.
A data pad electrode 41 is formed at one end of the data line 39 and has a larger width than that of the data line 39.
The gate pad electrode 27 and the data pad electrode 41 electrically contact with a transparent gate pad terminal electrode 63 and a transparent data pad terminal electrode 65, respectively. The transparent data pad terminal electrode 63 and the transparent data pad terminal electrode 65 directly receive corresponding external signals.
A storage capacitor C is formed on a portion of the gate line 25.
The TFT T includes a gate electrode 23, source/drain electrodes 35 and 37, and an active layer 31 formed on the gate electrode 23.
A transparent electrode 61 and a reflective electrode 49 with a transmission hole A are formed in the pixel region P. The transparent electrode 61 and the reflective electrode 49 define a transmission region B and a reflection region D.
The storage capacitor C includes a first capacitor electrode and a second capacitor electrode. A portion of the gate line 25 is used as the first capacitor electrode 43. A metal layer 43 facing a portion of the gate line 25 and formed on an equal layer to the drain electrode 37 is used as the second capacitor electrode.
The metal layer 43 may be connected to the transparent electrode 61 through a contact hole 55, or may be formed in the drain electrode 37 by extending above the gate line 25 through a lower portion of the reflective electrode 49. In this case, the contact hole 55 is not required.
FIG. 4 is a sectional view taken along lines II-II′, III-III′and IV-IV′ of FIG. 3 in the bottom substrate of the related art transflective type LCD.
Referring to FIG. 4, a gate electrode 23, a gate line 25, and a gate pad electrode 27 are formed on a substrate 21. The gate pad electrode 27 is connected to one end of the gate line 25.
A gate insulation layer 29 as a first insulation layer is formed on the substrate 21 where the gate electrode 23 and the gate line 25 are formed.
An active layer 31 and an ohmic contact layer 33 are formed in an island shape on the gate insulation layer 29 disposed on the gate electrode 23.
Source/drain electrodes 35 and 37 contacting the ohmic contact layer 33, a data line 39 connected to the source electrode 35, and a data pad electrode 41 connected to one end of the data line 39 are formed on the substrate 21 where the ohmic contact layer 33 is formed.
At the same time, an island-shaped metal layer 43 is formed on a portion of the gate line 25.
A protection layer 45 as a second insulation layer is formed on the substrate 21 where the data line 39 is formed.
The protection layer 45 is an inorganic insulation layer formed by depositing silicon nitride (SiNx) or silicon oxide (SiO2).
An organic insulation layer 47 is coated on the protection layer 45 to form a third insulation layer. The organic insulation layer 47 may be selected from the transparent organic insulation material group including benzo-cyclo-butene (BCB) and acryl-based resin.
A protrusion pattern 47b is formed in the reflection region D of the organic insulation layer 47.
The gate insulation layer 29, the protection layer 45, and the organic insulation layer 47 are etched to form an etch groove 48 in a portion of the pixel region P.
The etch groove 48 is a portion corresponding to the transmission hole of the reflective electrode that will be formed later.
Meanwhile, the protection layer 45 and the organic insulation layer 47 that dare disposed above the drain electrode 37, the metal layer 43, and the protection layer 45, and the gate insulation layer 29, the protection layer 45 and the organic insulation layer 47 that are disposed above the gate pad electrode 27, are etched to form a drain contact hole 53 exposing a portion of the drain electrode 37, a storage contact hole 55 exposing a portion of the metal layer 43, a gate pad contact hole 57 exposing a portion of the gate pad electrode 27, and a data pad contact hole 59 exposing a portion of the data pad electrode 41.
A transparent conductive metal including indium tin oxide (ITO) and indium zinc oxide (IZO) is deposited on the substrate 21 where the plurality of contact holes, 53, 55, 57, and 59 are formed and is patterned to form a transparent electrode 61 constituting the pixel region P while contacting the drain electrode 37 and the metal layer 43 at the same time, a gate pad terminal electrode 63 contacting the gate pad electrode 27, and a data pad terminal electrode 65 contacting the data pad electrode 41.
The transparent electrode 61 is also formed in a protrusion structure along the protrusion pattern 47b of the organic insulation layer 47 in the reflection region D.
A metal, such as aluminum or aluminum alloy, having an excellent reflectivity is deposited on the substrate 21 where the transparent electrode 61 is formed, and is patterned to form a reflective electrode 49 with a transmission hole A corresponding to the etch groove 48. The reflective electrode 49 is not formed at the bottom of the transmission hole A.
The reflective electrode 49 is formed along the organic insulation layer 47 and the transparent electrode 61 in the reflection region D to have protrusions corresponding to the protrusions in the organic insulation layer 47.
The bottom substrate of the related art transflective type LCD may be manufactured using the above-described method.
However, when the etching process is carried out for forming the reflective electrode 49 on the bottom substrate, the etching solution may penetrate the transparent electrode 61, the gate pad terminal electrode 63, and the data pad terminal electrode 65, resulting in defects.
In addition, due to the protrusion pattern 47b formed in the reflection region D, a problem of adhesion failure between the protrusion pattern-47b and the transparent electrode 61 is caused.
Further, when the gate insulation layer 29, the protection layer 45, and the organic insulation layer 47 are etched to form the transmission hole A, these layers may be over-etching the substrate 21. Therefore, when the transparent electrode 61 is formed in the transmission hole A, a problem occurs in that the transparent electrode 61 is badly deposited.